The present invention is related to removable shielding for use during neurological examinations on a whole body positron emission tomography scanner. More specifically, the present invention relates to removable neck shielding for use during neurological examinations on a whole body positron emission tomography scanner.
Positron emission tomography (PET) has evolved as a valuable technique for mapping the human brain and in providing the most specific imaging modality for the detection and staging of cancer. Many PET centres do a mix of these two types of imaging, but the optimal requirements for these modalities is very different. Brain mapping is performed using O15 water as a tracer, with many studies of about 1 minute scanning time on the same subject under differing conditions of brain activation. Whole body scans for cancer detection use the F18-fluoro-deoxyglucose as a tracer. Its 110 minute half-life allows for longer scans, typically 1 to 2 hours per patient. The high count-rates encountered during water studies imply they are severely contaminated by noise due to random and scattered counts. This noise can be reduced by improving the shielding of the detectors from activity in the rest of the body. In the Computer Technology and Imaging (CTI) HR+ scanner at the Montreal Neurological Institute (MNI) a permanent shield had been installed. This device, even though provided by the manufacturer, is not approved for use in the USA, and to minimize the risk of harm to the patients in scanners where it is installed, limit switches, and mechanical xe2x80x9cstopsxe2x80x9d are added to couch to prevent the axial drive motor extending the couch into the gantry. These safety devices prevent the scanner being used for oncology studies, if these involve imaging other organs besides the brain.
Positron emission tomography (PET) is a technique in the field of Nuclear Medicine which allows for xe2x80x9cFunctional Imagingxe2x80x9d where the intensity of the signal from different body parts is proportional to the rate at which it is working. It is used for mapping regions of the brain which are involved in performing certain tasks, in measuring which parts of the heart are lacking in blood supply or have enough blood but are not able to function correctly, and in distinguishing fast growing tumours from normal healthy tissue. The first application is mostly of interest to those studying the brain and the inter-relationship between its many parts. The second is currently the best way of deciding whether a patient would benefit from cardiac bypass surgery or grafting, or would require a heart transplant. The third, (and this is a very fast growing application at present) allows a fairly rapid and presently the most accurate assessment of the possibility of distant metastases which often occur in cancer). Almost as many PET scanners were purchased in 1999 as there were in the period up until then. This is mostly due to the fact that it is possible to get reimbursement of PET scans from most health insurance providers. Although it is the most expensive way to diagnose cancer, it is the most accurate, and the cost is justified on the basis of the cost of not treating the disease appropriately as soon as its presence has been recognized.
Early PET scanner had one ring of detectors and these were shielded with thick cylindrical sheets of lead which very effectively prevented gamma rays from outside the body section being imaged from reaching the detectors. In the 80""s and early 90""s scanners with several rings of detectors were developed and these had thin lead cylindrical sheets between each ring of detectors. In order to record a useful xe2x80x9ceventxe2x80x9d (and these events, millions of them, are used to form the image) one must observe the near-simultaneous detection of two gamma rays which are produced by the annihilation of a positron and an electron which occurs very close to and soon after a positron emitting isotope decays. The gamma rays are emitted at 180 degrees apart, but the line along which they travel in opposite directions is randomly orientated. Since these gamma rays do not emerge in the planes formed by the rings of detectors and the lead septa, most of the events are not detected in this geometry. Recently most PET scanners have sets of septa which can be retracted, or none at all. These are much more efficient (about 10 times more), but are about 50 times more efficient in the detection of scattered radiation which is both within and outside the field of view. Improved reconstruction and scattered radiation algorithms have been developed to deal with this increase in image signal and greater increase in unwanted information.
There has been quite a lot of work to reduce the effect of the unwanted radiation from outside the field of view. In some scanners, it is possible to purchase what the manufacturer calls the xe2x80x9cNeurological Insertxe2x80x9d. The advantage is that it performs much higher quality brain studies by reducing the out-of-field radiation very effectively. This is because the diameter through which the head goes is much smaller than the diameter of the hole required for the body to pass through. However, this and the one described in the paper by Hasegawa require turning off the scanner""s power, removal of the front cover of the scanner half an hour""s work, replacement of the front cover and temperature stabilization of the scanner. This is considered a service function, which some PET centers perform themselves, while others have a serviceman do the work. It is thus not a practical solution which would provide superior image quality when doing brain studies mixed in with whole body studies.
The present invention provides similar shielding properties than the xe2x80x9cpermanentxe2x80x9d Neurological Insert, and can be removed if required. However, it is NOT necessary to remove it to do cardiac scans, or for most oncology studies. It would only need to be removed for examining patients with xe2x80x9chead and neckxe2x80x9d cancer where a whole body scan is also needed.
The present invention pertains to a shielding system for a scanner. The system comprises a headrest. The system comprises shielding attached to the headrest. The system comprises a scanner couch to which the headrest is attached. The headrest moves with the scanner couch into the scanner.
The present invention pertains to a method for scanning a patient. The method comprises the steps of connecting a headrest with shielding to a couch. There is the step of moving the couch with the headrest into an opening of the scanner so the shielding blocks the opening.
The present invention pertains to a headrest for a couch of a scanner. The headrest comprises a head support. The headrest comprises a support from which the head support extends. The headrest comprises shielding connected to the support. The headrest comprises a backing extending from the support.
It is well known that the shielding against out-of-field scattered radiation is not very effective on whole body PET scanners operated with their slice-defining septa retracted. Additional shielding can be employed during neurological studies since the diameter of the head is much less than the field of view required for imaging the human torso. A new lead-plate shielding system which mounts on the scanner""s removable head-rest has been designed, built and tested (on the CTI HR+ PET scanner). This device is called the xe2x80x9cNeuroShieldxe2x80x9d. The outer diameter of the 9 mm thick lead plate is 550 mm which has a xe2x80x9cUxe2x80x9d shaped hole 220 mm in diameter. It is positioned just above the subject""s shoulders. A molded plastic coupling piece, produced by stereo-lithography, was designed to accommodate the complex shape of the headrest under the subject""s neck, and provide a flat surface for mounting the lead plate. Our testing on human subjects involved comparing the prompt and random count rates and dead time during bolus-water activation studies. Scans on different subjects, (matched for age and sex) with no additional shielding, with the CTI Neurological Insert, and with the NeuroShield were compared. The random counts were reduced by a factor of 1.56 when using the permanent CTI Neurological Insert, and 1.44 using the NeuroShield. The NeuroShield is easily removed to allow whole body scanning. It can remain in place as the couch extends through the scanning tunnel in the gantry. Its main application will be at PET centers doing a mixture of whole body and neurological studies, where the CTI Neurological Insert cannot be installed permanently.